This invention relates to strain measuring systems for measuring strain in a body subjected to variable stress, and, more particularly, to a fluid pressure strain measuring system.
Strain measuring systems have been in use for some time for measuring variable quantities such as strain, pressure, torque, acceleration and temperature. Such systems typically comprise a resistance wire connected in a conventional four-arm bridge circuit which ordinarily is balanced. The force to be measured is coupled mechanically to the resistance wire such that the force exerted on the wire through the coupling means causes the dimensions of the wire to be altered, which results in a proportional change in the resistance of the wire. This change in resistance in turn causes unbalancing of the bridge circuit in an amount proportional to the force applied to the wire. Such resistance wire filament strain measuring systems provide satisfactory results at ambient and moderately high temperatures because either the temperature induced variations of resistance are not significant or temperature compensation is feasible. However, in recent years in the testing and development of devices in the rocketry and missile fields, where temperatures in the thousands of degrees are encountered, the known temperature compensation techniques have not met the demands of these extremely high temperature applications.
Accordingly, it is an object of the present invention to provide a strain measuring system useful at extremely high temperatures.
It is a further object of the present invention to provide a strain measuring system using a fluid pressure strain-responsive bridge circuit to measure strains in extremely high temperature applications.
The present invention is summarized in that a strain measuring system comprises four strain-responsive tubes arranged in bridge circuit fashion and carrying at a constant flow rate and pressure a fluid stream so that a strain caused deformation of the strain-responsive tubes causes a change in fluid flow which is proportional to the strain.